diff options
Diffstat (limited to 'lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp | 633 |
1 files changed, 421 insertions, 212 deletions
diff --git a/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp b/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp index b8529e1..62f2026 100644 --- a/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp +++ b/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp @@ -121,41 +121,75 @@ class ConstantOffsetExtractor { /// numeric value of the extracted constant offset (0 if failed), and a /// new index representing the remainder (equal to the original index minus /// the constant offset). - /// \p Idx The given GEP index - /// \p NewIdx The new index to replace - /// \p DL The datalayout of the module - /// \p IP Calculating the new index requires new instructions. IP indicates - /// where to insert them (typically right before the GEP). + /// \p Idx The given GEP index + /// \p NewIdx The new index to replace (output) + /// \p DL The datalayout of the module + /// \p GEP The given GEP static int64_t Extract(Value *Idx, Value *&NewIdx, const DataLayout *DL, - Instruction *IP); + GetElementPtrInst *GEP); /// Looks for a constant offset without extracting it. The meaning of the /// arguments and the return value are the same as Extract. - static int64_t Find(Value *Idx, const DataLayout *DL); + static int64_t Find(Value *Idx, const DataLayout *DL, GetElementPtrInst *GEP); private: ConstantOffsetExtractor(const DataLayout *Layout, Instruction *InsertionPt) : DL(Layout), IP(InsertionPt) {} - /// Searches the expression that computes V for a constant offset. If the - /// searching is successful, update UserChain as a path from V to the constant - /// offset. - int64_t find(Value *V); - /// A helper function to look into both operands of a binary operator U. - /// \p IsSub Whether U is a sub operator. If so, we need to negate the - /// constant offset at some point. - int64_t findInEitherOperand(User *U, bool IsSub); - /// After finding the constant offset and how it is reached from the GEP - /// index, we build a new index which is a clone of the old one except the - /// constant offset is removed. For example, given (a + (b + 5)) and knowning - /// the constant offset is 5, this function returns (a + b). + /// Searches the expression that computes V for a non-zero constant C s.t. + /// V can be reassociated into the form V' + C. If the searching is + /// successful, returns C and update UserChain as a def-use chain from C to V; + /// otherwise, UserChain is empty. /// - /// We cannot simply change the constant to zero because the expression that - /// computes the index or its intermediate result may be used by others. - Value *rebuildWithoutConstantOffset(); - // A helper function for rebuildWithoutConstantOffset that rebuilds the direct - // user (U) of the constant offset (C). - Value *rebuildLeafWithoutConstantOffset(User *U, Value *C); - /// Returns a clone of U except the first occurrence of From with To. - Value *cloneAndReplace(User *U, Value *From, Value *To); + /// \p V The given expression + /// \p SignExtended Whether V will be sign-extended in the computation of the + /// GEP index + /// \p ZeroExtended Whether V will be zero-extended in the computation of the + /// GEP index + /// \p NonNegative Whether V is guaranteed to be non-negative. For example, + /// an index of an inbounds GEP is guaranteed to be + /// non-negative. Levaraging this, we can better split + /// inbounds GEPs. + APInt find(Value *V, bool SignExtended, bool ZeroExtended, bool NonNegative); + /// A helper function to look into both operands of a binary operator. + APInt findInEitherOperand(BinaryOperator *BO, bool SignExtended, + bool ZeroExtended); + /// After finding the constant offset C from the GEP index I, we build a new + /// index I' s.t. I' + C = I. This function builds and returns the new + /// index I' according to UserChain produced by function "find". + /// + /// The building conceptually takes two steps: + /// 1) iteratively distribute s/zext towards the leaves of the expression tree + /// that computes I + /// 2) reassociate the expression tree to the form I' + C. + /// + /// For example, to extract the 5 from sext(a + (b + 5)), we first distribute + /// sext to a, b and 5 so that we have + /// sext(a) + (sext(b) + 5). + /// Then, we reassociate it to + /// (sext(a) + sext(b)) + 5. + /// Given this form, we know I' is sext(a) + sext(b). + Value *rebuildWithoutConstOffset(); + /// After the first step of rebuilding the GEP index without the constant + /// offset, distribute s/zext to the operands of all operators in UserChain. + /// e.g., zext(sext(a + (b + 5)) (assuming no overflow) => + /// zext(sext(a)) + (zext(sext(b)) + zext(sext(5))). + /// + /// The function also updates UserChain to point to new subexpressions after + /// distributing s/zext. e.g., the old UserChain of the above example is + /// 5 -> b + 5 -> a + (b + 5) -> sext(...) -> zext(sext(...)), + /// and the new UserChain is + /// zext(sext(5)) -> zext(sext(b)) + zext(sext(5)) -> + /// zext(sext(a)) + (zext(sext(b)) + zext(sext(5)) + /// + /// \p ChainIndex The index to UserChain. ChainIndex is initially + /// UserChain.size() - 1, and is decremented during + /// the recursion. + Value *distributeExtsAndCloneChain(unsigned ChainIndex); + /// Reassociates the GEP index to the form I' + C and returns I'. + Value *removeConstOffset(unsigned ChainIndex); + /// A helper function to apply ExtInsts, a list of s/zext, to value V. + /// e.g., if ExtInsts = [sext i32 to i64, zext i16 to i32], this function + /// returns "sext i32 (zext i16 V to i32) to i64". + Value *applyExts(Value *V); /// Returns true if LHS and RHS have no bits in common, i.e., LHS | RHS == 0. bool NoCommonBits(Value *LHS, Value *RHS) const; @@ -163,20 +197,26 @@ class ConstantOffsetExtractor { /// \p KnownOne Mask of all bits that are known to be one. /// \p KnownZero Mask of all bits that are known to be zero. void ComputeKnownBits(Value *V, APInt &KnownOne, APInt &KnownZero) const; - /// Finds the first use of Used in U. Returns -1 if not found. - static unsigned FindFirstUse(User *U, Value *Used); - /// Returns whether OPC (sext or zext) can be distributed to the operands of - /// BO. e.g., sext can be distributed to the operands of an "add nsw" because - /// sext (add nsw a, b) == add nsw (sext a), (sext b). - static bool Distributable(unsigned OPC, BinaryOperator *BO); + /// A helper function that returns whether we can trace into the operands + /// of binary operator BO for a constant offset. + /// + /// \p SignExtended Whether BO is surrounded by sext + /// \p ZeroExtended Whether BO is surrounded by zext + /// \p NonNegative Whether BO is known to be non-negative, e.g., an in-bound + /// array index. + bool CanTraceInto(bool SignExtended, bool ZeroExtended, BinaryOperator *BO, + bool NonNegative); /// The path from the constant offset to the old GEP index. e.g., if the GEP /// index is "a * b + (c + 5)". After running function find, UserChain[0] will /// be the constant 5, UserChain[1] will be the subexpression "c + 5", and /// UserChain[2] will be the entire expression "a * b + (c + 5)". /// - /// This path helps rebuildWithoutConstantOffset rebuild the new GEP index. + /// This path helps to rebuild the new GEP index. SmallVector<User *, 8> UserChain; + /// A data structure used in rebuildWithoutConstOffset. Contains all + /// sext/zext instructions along UserChain. + SmallVector<CastInst *, 16> ExtInsts; /// The data layout of the module. Used in ComputeKnownBits. const DataLayout *DL; Instruction *IP; /// Insertion position of cloned instructions. @@ -196,6 +236,15 @@ class SeparateConstOffsetFromGEP : public FunctionPass { AU.addRequired<DataLayoutPass>(); AU.addRequired<TargetTransformInfo>(); } + + bool doInitialization(Module &M) override { + DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); + if (DLP == nullptr) + report_fatal_error("data layout missing"); + DL = &DLP->getDataLayout(); + return false; + } + bool runOnFunction(Function &F) override; private: @@ -206,8 +255,42 @@ class SeparateConstOffsetFromGEP : public FunctionPass { /// function only inspects the GEP without changing it. The output /// NeedsExtraction indicates whether we can extract a non-zero constant /// offset from any index. - int64_t accumulateByteOffset(GetElementPtrInst *GEP, const DataLayout *DL, - bool &NeedsExtraction); + int64_t accumulateByteOffset(GetElementPtrInst *GEP, bool &NeedsExtraction); + /// Canonicalize array indices to pointer-size integers. This helps to + /// simplify the logic of splitting a GEP. For example, if a + b is a + /// pointer-size integer, we have + /// gep base, a + b = gep (gep base, a), b + /// However, this equality may not hold if the size of a + b is smaller than + /// the pointer size, because LLVM conceptually sign-extends GEP indices to + /// pointer size before computing the address + /// (http://llvm.org/docs/LangRef.html#id181). + /// + /// This canonicalization is very likely already done in clang and + /// instcombine. Therefore, the program will probably remain the same. + /// + /// Returns true if the module changes. + /// + /// Verified in @i32_add in split-gep.ll + bool canonicalizeArrayIndicesToPointerSize(GetElementPtrInst *GEP); + /// For each array index that is in the form of zext(a), convert it to sext(a) + /// if we can prove zext(a) <= max signed value of typeof(a). We prefer + /// sext(a) to zext(a), because in the special case where x + y >= 0 and + /// (x >= 0 or y >= 0), function CanTraceInto can split sext(x + y), + /// while no such case exists for zext(x + y). + /// + /// Note that + /// zext(x + y) = zext(x) + zext(y) + /// is wrong, e.g., + /// zext i32(UINT_MAX + 1) to i64 != + /// (zext i32 UINT_MAX to i64) + (zext i32 1 to i64) + /// + /// Returns true if the module changes. + /// + /// Verified in @inbounds_zext_add in split-gep.ll and @sum_of_array3 in + /// split-gep-and-gvn.ll + bool convertInBoundsZExtToSExt(GetElementPtrInst *GEP); + + const DataLayout *DL; }; } // anonymous namespace @@ -227,181 +310,272 @@ FunctionPass *llvm::createSeparateConstOffsetFromGEPPass() { return new SeparateConstOffsetFromGEP(); } -bool ConstantOffsetExtractor::Distributable(unsigned OPC, BinaryOperator *BO) { - assert(OPC == Instruction::SExt || OPC == Instruction::ZExt); +bool ConstantOffsetExtractor::CanTraceInto(bool SignExtended, + bool ZeroExtended, + BinaryOperator *BO, + bool NonNegative) { + // We only consider ADD, SUB and OR, because a non-zero constant found in + // expressions composed of these operations can be easily hoisted as a + // constant offset by reassociation. + if (BO->getOpcode() != Instruction::Add && + BO->getOpcode() != Instruction::Sub && + BO->getOpcode() != Instruction::Or) { + return false; + } + + Value *LHS = BO->getOperand(0), *RHS = BO->getOperand(1); + // Do not trace into "or" unless it is equivalent to "add". If LHS and RHS + // don't have common bits, (LHS | RHS) is equivalent to (LHS + RHS). + if (BO->getOpcode() == Instruction::Or && !NoCommonBits(LHS, RHS)) + return false; + + // In addition, tracing into BO requires that its surrounding s/zext (if + // any) is distributable to both operands. + // + // Suppose BO = A op B. + // SignExtended | ZeroExtended | Distributable? + // --------------+--------------+---------------------------------- + // 0 | 0 | true because no s/zext exists + // 0 | 1 | zext(BO) == zext(A) op zext(B) + // 1 | 0 | sext(BO) == sext(A) op sext(B) + // 1 | 1 | zext(sext(BO)) == + // | | zext(sext(A)) op zext(sext(B)) + if (BO->getOpcode() == Instruction::Add && !ZeroExtended && NonNegative) { + // If a + b >= 0 and (a >= 0 or b >= 0), then + // sext(a + b) = sext(a) + sext(b) + // even if the addition is not marked nsw. + // + // Leveraging this invarient, we can trace into an sext'ed inbound GEP + // index if the constant offset is non-negative. + // + // Verified in @sext_add in split-gep.ll. + if (ConstantInt *ConstLHS = dyn_cast<ConstantInt>(LHS)) { + if (!ConstLHS->isNegative()) + return true; + } + if (ConstantInt *ConstRHS = dyn_cast<ConstantInt>(RHS)) { + if (!ConstRHS->isNegative()) + return true; + } + } // sext (add/sub nsw A, B) == add/sub nsw (sext A), (sext B) // zext (add/sub nuw A, B) == add/sub nuw (zext A), (zext B) if (BO->getOpcode() == Instruction::Add || BO->getOpcode() == Instruction::Sub) { - return (OPC == Instruction::SExt && BO->hasNoSignedWrap()) || - (OPC == Instruction::ZExt && BO->hasNoUnsignedWrap()); + if (SignExtended && !BO->hasNoSignedWrap()) + return false; + if (ZeroExtended && !BO->hasNoUnsignedWrap()) + return false; } - // sext/zext (and/or/xor A, B) == and/or/xor (sext/zext A), (sext/zext B) - // -instcombine also leverages this invariant to do the reverse - // transformation to reduce integer casts. - return BO->getOpcode() == Instruction::And || - BO->getOpcode() == Instruction::Or || - BO->getOpcode() == Instruction::Xor; + return true; } -int64_t ConstantOffsetExtractor::findInEitherOperand(User *U, bool IsSub) { - assert(U->getNumOperands() == 2); - int64_t ConstantOffset = find(U->getOperand(0)); +APInt ConstantOffsetExtractor::findInEitherOperand(BinaryOperator *BO, + bool SignExtended, + bool ZeroExtended) { + // BO being non-negative does not shed light on whether its operands are + // non-negative. Clear the NonNegative flag here. + APInt ConstantOffset = find(BO->getOperand(0), SignExtended, ZeroExtended, + /* NonNegative */ false); // If we found a constant offset in the left operand, stop and return that. // This shortcut might cause us to miss opportunities of combining the // constant offsets in both operands, e.g., (a + 4) + (b + 5) => (a + b) + 9. // However, such cases are probably already handled by -instcombine, // given this pass runs after the standard optimizations. if (ConstantOffset != 0) return ConstantOffset; - ConstantOffset = find(U->getOperand(1)); + ConstantOffset = find(BO->getOperand(1), SignExtended, ZeroExtended, + /* NonNegative */ false); // If U is a sub operator, negate the constant offset found in the right // operand. - return IsSub ? -ConstantOffset : ConstantOffset; + if (BO->getOpcode() == Instruction::Sub) + ConstantOffset = -ConstantOffset; + return ConstantOffset; } -int64_t ConstantOffsetExtractor::find(Value *V) { - // TODO(jingyue): We can even trace into integer/pointer casts, such as +APInt ConstantOffsetExtractor::find(Value *V, bool SignExtended, + bool ZeroExtended, bool NonNegative) { + // TODO(jingyue): We could trace into integer/pointer casts, such as // inttoptr, ptrtoint, bitcast, and addrspacecast. We choose to handle only // integers because it gives good enough results for our benchmarks. - assert(V->getType()->isIntegerTy()); + unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth(); + // We cannot do much with Values that are not a User, such as an Argument. User *U = dyn_cast<User>(V); - // We cannot do much with Values that are not a User, such as BasicBlock and - // MDNode. - if (U == nullptr) return 0; + if (U == nullptr) return APInt(BitWidth, 0); - int64_t ConstantOffset = 0; - if (ConstantInt *CI = dyn_cast<ConstantInt>(U)) { + APInt ConstantOffset(BitWidth, 0); + if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { // Hooray, we found it! - ConstantOffset = CI->getSExtValue(); - } else if (Operator *O = dyn_cast<Operator>(U)) { - // The GEP index may be more complicated than a simple addition of a - // varaible and a constant. Therefore, we trace into subexpressions for more - // hoisting opportunities. - switch (O->getOpcode()) { - case Instruction::Add: { - ConstantOffset = findInEitherOperand(U, false); - break; - } - case Instruction::Sub: { - ConstantOffset = findInEitherOperand(U, true); - break; - } - case Instruction::Or: { - // If LHS and RHS don't have common bits, (LHS | RHS) is equivalent to - // (LHS + RHS). - if (NoCommonBits(U->getOperand(0), U->getOperand(1))) - ConstantOffset = findInEitherOperand(U, false); - break; - } - case Instruction::SExt: - case Instruction::ZExt: { - // We trace into sext/zext if the operator can be distributed to its - // operand. e.g., we can transform into "sext (add nsw a, 5)" and - // extract constant 5, because - // sext (add nsw a, 5) == add nsw (sext a), 5 - if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) { - if (Distributable(O->getOpcode(), BO)) - ConstantOffset = find(U->getOperand(0)); - } - break; - } + ConstantOffset = CI->getValue(); + } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V)) { + // Trace into subexpressions for more hoisting opportunities. + if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative)) { + ConstantOffset = findInEitherOperand(BO, SignExtended, ZeroExtended); } + } else if (isa<SExtInst>(V)) { + ConstantOffset = find(U->getOperand(0), /* SignExtended */ true, + ZeroExtended, NonNegative).sext(BitWidth); + } else if (isa<ZExtInst>(V)) { + // As an optimization, we can clear the SignExtended flag because + // sext(zext(a)) = zext(a). Verified in @sext_zext in split-gep.ll. + // + // Clear the NonNegative flag, because zext(a) >= 0 does not imply a >= 0. + ConstantOffset = + find(U->getOperand(0), /* SignExtended */ false, + /* ZeroExtended */ true, /* NonNegative */ false).zext(BitWidth); } - // If we found a non-zero constant offset, adds it to the path for future - // transformation (rebuildWithoutConstantOffset). Zero is a valid constant - // offset, but doesn't help this optimization. + + // If we found a non-zero constant offset, add it to the path for + // rebuildWithoutConstOffset. Zero is a valid constant offset, but doesn't + // help this optimization. if (ConstantOffset != 0) UserChain.push_back(U); return ConstantOffset; } -unsigned ConstantOffsetExtractor::FindFirstUse(User *U, Value *Used) { - for (unsigned I = 0, E = U->getNumOperands(); I < E; ++I) { - if (U->getOperand(I) == Used) - return I; +Value *ConstantOffsetExtractor::applyExts(Value *V) { + Value *Current = V; + // ExtInsts is built in the use-def order. Therefore, we apply them to V + // in the reversed order. + for (auto I = ExtInsts.rbegin(), E = ExtInsts.rend(); I != E; ++I) { + if (Constant *C = dyn_cast<Constant>(Current)) { + // If Current is a constant, apply s/zext using ConstantExpr::getCast. + // ConstantExpr::getCast emits a ConstantInt if C is a ConstantInt. + Current = ConstantExpr::getCast((*I)->getOpcode(), C, (*I)->getType()); + } else { + Instruction *Ext = (*I)->clone(); + Ext->setOperand(0, Current); + Ext->insertBefore(IP); + Current = Ext; + } } - return -1; + return Current; } -Value *ConstantOffsetExtractor::cloneAndReplace(User *U, Value *From, - Value *To) { - // Finds in U the first use of From. It is safe to ignore future occurrences - // of From, because findInEitherOperand similarly stops searching the right - // operand when the first operand has a non-zero constant offset. - unsigned OpNo = FindFirstUse(U, From); - assert(OpNo != (unsigned)-1 && "UserChain wasn't built correctly"); - - // ConstantOffsetExtractor::find only follows Operators (i.e., Instructions - // and ConstantExprs). Therefore, U is either an Instruction or a - // ConstantExpr. - if (Instruction *I = dyn_cast<Instruction>(U)) { - Instruction *Clone = I->clone(); - Clone->setOperand(OpNo, To); - Clone->insertBefore(IP); - return Clone; +Value *ConstantOffsetExtractor::rebuildWithoutConstOffset() { + distributeExtsAndCloneChain(UserChain.size() - 1); + // Remove all nullptrs (used to be s/zext) from UserChain. + unsigned NewSize = 0; + for (auto I = UserChain.begin(), E = UserChain.end(); I != E; ++I) { + if (*I != nullptr) { + UserChain[NewSize] = *I; + NewSize++; + } } - // cast<Constant>(To) is safe because a ConstantExpr only uses Constants. - return cast<ConstantExpr>(U) - ->getWithOperandReplaced(OpNo, cast<Constant>(To)); + UserChain.resize(NewSize); + return removeConstOffset(UserChain.size() - 1); } -Value *ConstantOffsetExtractor::rebuildLeafWithoutConstantOffset(User *U, - Value *C) { - assert(U->getNumOperands() <= 2 && - "We didn't trace into any operator with more than 2 operands"); - // If U has only one operand which is the constant offset, removing the - // constant offset leaves U as a null value. - if (U->getNumOperands() == 1) - return Constant::getNullValue(U->getType()); - - // U->getNumOperands() == 2 - unsigned OpNo = FindFirstUse(U, C); // U->getOperand(OpNo) == C - assert(OpNo < 2 && "UserChain wasn't built correctly"); - Value *TheOther = U->getOperand(1 - OpNo); // The other operand of U - // If U = C - X, removing C makes U = -X; otherwise U will simply be X. - if (!isa<SubOperator>(U) || OpNo == 1) - return TheOther; - if (isa<ConstantExpr>(U)) - return ConstantExpr::getNeg(cast<Constant>(TheOther)); - return BinaryOperator::CreateNeg(TheOther, "", IP); +Value * +ConstantOffsetExtractor::distributeExtsAndCloneChain(unsigned ChainIndex) { + User *U = UserChain[ChainIndex]; + if (ChainIndex == 0) { + assert(isa<ConstantInt>(U)); + // If U is a ConstantInt, applyExts will return a ConstantInt as well. + return UserChain[ChainIndex] = cast<ConstantInt>(applyExts(U)); + } + + if (CastInst *Cast = dyn_cast<CastInst>(U)) { + assert((isa<SExtInst>(Cast) || isa<ZExtInst>(Cast)) && + "We only traced into two types of CastInst: sext and zext"); + ExtInsts.push_back(Cast); + UserChain[ChainIndex] = nullptr; + return distributeExtsAndCloneChain(ChainIndex - 1); + } + + // Function find only trace into BinaryOperator and CastInst. + BinaryOperator *BO = cast<BinaryOperator>(U); + // OpNo = which operand of BO is UserChain[ChainIndex - 1] + unsigned OpNo = (BO->getOperand(0) == UserChain[ChainIndex - 1] ? 0 : 1); + Value *TheOther = applyExts(BO->getOperand(1 - OpNo)); + Value *NextInChain = distributeExtsAndCloneChain(ChainIndex - 1); + + BinaryOperator *NewBO = nullptr; + if (OpNo == 0) { + NewBO = BinaryOperator::Create(BO->getOpcode(), NextInChain, TheOther, + BO->getName(), IP); + } else { + NewBO = BinaryOperator::Create(BO->getOpcode(), TheOther, NextInChain, + BO->getName(), IP); + } + return UserChain[ChainIndex] = NewBO; } -Value *ConstantOffsetExtractor::rebuildWithoutConstantOffset() { - assert(UserChain.size() > 0 && "you at least found a constant, right?"); - // Start with the constant and go up through UserChain, each time building a - // clone of the subexpression but with the constant removed. - // e.g., to build a clone of (a + (b + (c + 5)) but with the 5 removed, we - // first c, then (b + c), and finally (a + (b + c)). - // - // Fast path: if the GEP index is a constant, simply returns 0. - if (UserChain.size() == 1) - return ConstantInt::get(UserChain[0]->getType(), 0); - - Value *Remainder = - rebuildLeafWithoutConstantOffset(UserChain[1], UserChain[0]); - for (size_t I = 2; I < UserChain.size(); ++I) - Remainder = cloneAndReplace(UserChain[I], UserChain[I - 1], Remainder); - return Remainder; +Value *ConstantOffsetExtractor::removeConstOffset(unsigned ChainIndex) { + if (ChainIndex == 0) { + assert(isa<ConstantInt>(UserChain[ChainIndex])); + return ConstantInt::getNullValue(UserChain[ChainIndex]->getType()); + } + + BinaryOperator *BO = cast<BinaryOperator>(UserChain[ChainIndex]); + unsigned OpNo = (BO->getOperand(0) == UserChain[ChainIndex - 1] ? 0 : 1); + assert(BO->getOperand(OpNo) == UserChain[ChainIndex - 1]); + Value *NextInChain = removeConstOffset(ChainIndex - 1); + Value *TheOther = BO->getOperand(1 - OpNo); + + // If NextInChain is 0 and not the LHS of a sub, we can simplify the + // sub-expression to be just TheOther. + if (ConstantInt *CI = dyn_cast<ConstantInt>(NextInChain)) { + if (CI->isZero() && !(BO->getOpcode() == Instruction::Sub && OpNo == 0)) + return TheOther; + } + + if (BO->getOpcode() == Instruction::Or) { + // Rebuild "or" as "add", because "or" may be invalid for the new + // epxression. + // + // For instance, given + // a | (b + 5) where a and b + 5 have no common bits, + // we can extract 5 as the constant offset. + // + // However, reusing the "or" in the new index would give us + // (a | b) + 5 + // which does not equal a | (b + 5). + // + // Replacing the "or" with "add" is fine, because + // a | (b + 5) = a + (b + 5) = (a + b) + 5 + return BinaryOperator::CreateAdd(BO->getOperand(0), BO->getOperand(1), + BO->getName(), IP); + } + + // We can reuse BO in this case, because the new expression shares the same + // instruction type and BO is used at most once. + assert(BO->getNumUses() <= 1 && + "distributeExtsAndCloneChain clones each BinaryOperator in " + "UserChain, so no one should be used more than " + "once"); + BO->setOperand(OpNo, NextInChain); + BO->setHasNoSignedWrap(false); + BO->setHasNoUnsignedWrap(false); + // Make sure it appears after all instructions we've inserted so far. + BO->moveBefore(IP); + return BO; } int64_t ConstantOffsetExtractor::Extract(Value *Idx, Value *&NewIdx, const DataLayout *DL, - Instruction *IP) { - ConstantOffsetExtractor Extractor(DL, IP); + GetElementPtrInst *GEP) { + ConstantOffsetExtractor Extractor(DL, GEP); // Find a non-zero constant offset first. - int64_t ConstantOffset = Extractor.find(Idx); - if (ConstantOffset == 0) - return 0; - // Then rebuild a new index with the constant removed. - NewIdx = Extractor.rebuildWithoutConstantOffset(); - return ConstantOffset; + APInt ConstantOffset = + Extractor.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false, + GEP->isInBounds()); + if (ConstantOffset != 0) { + // Separates the constant offset from the GEP index. + NewIdx = Extractor.rebuildWithoutConstOffset(); + } + return ConstantOffset.getSExtValue(); } -int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL) { - return ConstantOffsetExtractor(DL, nullptr).find(Idx); +int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL, + GetElementPtrInst *GEP) { + // If Idx is an index of an inbound GEP, Idx is guaranteed to be non-negative. + return ConstantOffsetExtractor(DL, GEP) + .find(Idx, /* SignExtended */ false, /* ZeroExtended */ false, + GEP->isInBounds()) + .getSExtValue(); } void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne, @@ -421,8 +595,64 @@ bool ConstantOffsetExtractor::NoCommonBits(Value *LHS, Value *RHS) const { return (LHSKnownZero | RHSKnownZero).isAllOnesValue(); } -int64_t SeparateConstOffsetFromGEP::accumulateByteOffset( - GetElementPtrInst *GEP, const DataLayout *DL, bool &NeedsExtraction) { +bool SeparateConstOffsetFromGEP::canonicalizeArrayIndicesToPointerSize( + GetElementPtrInst *GEP) { + bool Changed = false; + Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); + gep_type_iterator GTI = gep_type_begin(*GEP); + for (User::op_iterator I = GEP->op_begin() + 1, E = GEP->op_end(); + I != E; ++I, ++GTI) { + // Skip struct member indices which must be i32. + if (isa<SequentialType>(*GTI)) { + if ((*I)->getType() != IntPtrTy) { + *I = CastInst::CreateIntegerCast(*I, IntPtrTy, true, "idxprom", GEP); + Changed = true; + } + } + } + return Changed; +} + +bool +SeparateConstOffsetFromGEP::convertInBoundsZExtToSExt(GetElementPtrInst *GEP) { + if (!GEP->isInBounds()) + return false; + + // TODO: consider alloca + GlobalVariable *UnderlyingObject = + dyn_cast<GlobalVariable>(GEP->getPointerOperand()); + if (UnderlyingObject == nullptr) + return false; + + uint64_t ObjectSize = + DL->getTypeAllocSize(UnderlyingObject->getType()->getElementType()); + gep_type_iterator GTI = gep_type_begin(*GEP); + bool Changed = false; + for (User::op_iterator I = GEP->op_begin() + 1, E = GEP->op_end(); I != E; + ++I, ++GTI) { + if (isa<SequentialType>(*GTI)) { + if (ZExtInst *Extended = dyn_cast<ZExtInst>(*I)) { + unsigned SrcBitWidth = + cast<IntegerType>(Extended->getSrcTy())->getBitWidth(); + // For GEP operand zext(a), if a <= max signed value of typeof(a), then + // the sign bit of a is zero and sext(a) = zext(a). Because the GEP is + // in bounds, we know a <= ObjectSize, so the condition can be reduced + // to ObjectSize <= max signed value of typeof(a). + if (ObjectSize <= + APInt::getSignedMaxValue(SrcBitWidth).getZExtValue()) { + *I = new SExtInst(Extended->getOperand(0), Extended->getType(), + Extended->getName(), GEP); + Changed = true; + } + } + } + } + return Changed; +} + +int64_t +SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP, + bool &NeedsExtraction) { NeedsExtraction = false; int64_t AccumulativeByteOffset = 0; gep_type_iterator GTI = gep_type_begin(*GEP); @@ -430,7 +660,7 @@ int64_t SeparateConstOffsetFromGEP::accumulateByteOffset( if (isa<SequentialType>(*GTI)) { // Tries to extract a constant offset from this GEP index. int64_t ConstantOffset = - ConstantOffsetExtractor::Find(GEP->getOperand(I), DL); + ConstantOffsetExtractor::Find(GEP->getOperand(I), DL, GEP); if (ConstantOffset != 0) { NeedsExtraction = true; // A GEP may have multiple indices. We accumulate the extracted @@ -455,31 +685,11 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { return false; bool Changed = false; + Changed |= canonicalizeArrayIndicesToPointerSize(GEP); + Changed |= convertInBoundsZExtToSExt(GEP); - // Shortcuts integer casts. Eliminating these explicit casts can make - // subsequent optimizations more obvious: ConstantOffsetExtractor needn't - // trace into these casts. - if (GEP->isInBounds()) { - // Doing this to inbounds GEPs is safe because their indices are guaranteed - // to be non-negative and in bounds. - gep_type_iterator GTI = gep_type_begin(*GEP); - for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) { - if (isa<SequentialType>(*GTI)) { - if (Operator *O = dyn_cast<Operator>(GEP->getOperand(I))) { - if (O->getOpcode() == Instruction::SExt || - O->getOpcode() == Instruction::ZExt) { - GEP->setOperand(I, O->getOperand(0)); - Changed = true; - } - } - } - } - } - - const DataLayout *DL = &getAnalysis<DataLayoutPass>().getDataLayout(); bool NeedsExtraction; - int64_t AccumulativeByteOffset = - accumulateByteOffset(GEP, DL, NeedsExtraction); + int64_t AccumulativeByteOffset = accumulateByteOffset(GEP, NeedsExtraction); if (!NeedsExtraction) return Changed; @@ -506,30 +716,29 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { assert(NewIdx != nullptr && "ConstantOffset != 0 implies NewIdx is set"); GEP->setOperand(I, NewIdx); - // Clear the inbounds attribute because the new index may be off-bound. - // e.g., - // - // b = add i64 a, 5 - // addr = gep inbounds float* p, i64 b - // - // is transformed to: - // - // addr2 = gep float* p, i64 a - // addr = gep float* addr2, i64 5 - // - // If a is -4, although the old index b is in bounds, the new index a is - // off-bound. http://llvm.org/docs/LangRef.html#id181 says "if the - // inbounds keyword is not present, the offsets are added to the base - // address with silently-wrapping two's complement arithmetic". - // Therefore, the final code will be a semantically equivalent. - // - // TODO(jingyue): do some range analysis to keep as many inbounds as - // possible. GEPs with inbounds are more friendly to alias analysis. - GEP->setIsInBounds(false); - Changed = true; } } } + // Clear the inbounds attribute because the new index may be off-bound. + // e.g., + // + // b = add i64 a, 5 + // addr = gep inbounds float* p, i64 b + // + // is transformed to: + // + // addr2 = gep float* p, i64 a + // addr = gep float* addr2, i64 5 + // + // If a is -4, although the old index b is in bounds, the new index a is + // off-bound. http://llvm.org/docs/LangRef.html#id181 says "if the + // inbounds keyword is not present, the offsets are added to the base + // address with silently-wrapping two's complement arithmetic". + // Therefore, the final code will be a semantically equivalent. + // + // TODO(jingyue): do some range analysis to keep as many inbounds as + // possible. GEPs with inbounds are more friendly to alias analysis. + GEP->setIsInBounds(false); // Offsets the base with the accumulative byte offset. // @@ -562,9 +771,9 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { Instruction *NewGEP = GEP->clone(); NewGEP->insertBefore(GEP); - Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); uint64_t ElementTypeSizeOfGEP = DL->getTypeAllocSize(GEP->getType()->getElementType()); + Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); if (AccumulativeByteOffset % ElementTypeSizeOfGEP == 0) { // Very likely. As long as %gep is natually aligned, the byte offset we // extracted should be a multiple of sizeof(*%gep). |